Cancer Survivors Network

My sister is still waiting for a final diagnosis. Lymphoma is suspected but leukemia has not been ruled out. Can someone explain in layman's terms what a "fish test" is and what information that will provide that the other bone marrow tests did not.....why does this have to take so long....she was hospitalized on New Years day, and the results of the fish test will not be available for another 7-10 days.